1. Field of the Invention
The invention relates a method for manufacturing a combined solid immersion lens (SIL) and submicron aperture, and device thereof and, more specially, to a batch process for manufacturing a combined solid immersion lens (SIL) and nanometer aperture, which utilizes two photo mask steps incoporated with electroplating to combine a microlens structure with a nanometer order of aperture in order to manufacture an optical read/write apparatus having solid immersion lens and nanometer aperture with high resolution so as to increase optical storage density, and device thereof.
2. Related Arts of the Invention
The high density of optical data storage technologies has been currently a rapidly development and increasingly mature technology. Nowadays, there are already some commercial products like CD-ROM, MO, DVD and so forth utilized in multimedia or data storage. At present, the highest density of data storage in these commercial products performs just nearly 2 to 4.7 Gb/in2 in DVD technology. It means that there are still lots efforts to make the data storage density more advanced.
To get a higher storage density, the optical read/write apparatus (optical pick up head) must offer a small spot to reduce the size of data pits. In conventional optical pick up head, an objective lens is used to focus the light source such that the light source becomes a small spot to write or read data on the media. Among others, it is known that the numerical aperture (NA) and wavelength can dominate the spot size. Besides, it is also approved that a tiny aperture can restrict the spot size. For those reasons, the research here will put emphasis on the fabrications of lens and aperture to gain a smaller spot size.
In contrast with the conventional optical lens, the Solid Immersion Lens (SIL) using solid state technology gets the great performance in reducing spot size. The SIL was introduced by Mansfield and Kino in 1990 for use in high resolution microscopy (Appl. Phys. Lett.57(1990) 2615), and in 1994, Terris introduced the SIL for optical recording (Appl. Phys. Lett.65(1994) 388). As shown in FIG. 1, the FIG. 1 is a schematic drawing showing a conventionally optical read/write apparatus having combined SIL and aperture. The configuration of FIG. 1 can record the data in high density. The reference numerals of FIG. 1, 1 represents SIL, 2 indicates aperture, 3 is beam splitter, 4 is objective, 5 is laser beam, and 6 represents recording media. Typically, the diameter of the focused spot can be xcex/NA (where NA is the numerical aperture of the lens, i.e. NA=nxc3x97sinxcex8, xcex is the wavelength, n is the refractive index of where the spot is located, and xcex8 is the incident angle.), the greatest efficacy of the SIL is to increase the NA. Therefore, by using a lens material with high n and a possibly round shaped lens curvature, as well as an arrangement of near field to increase xcex8 for the increase of the NA, is indeed capable of reducing the spot size. It was known that the photoresist AZ-P4620 (n≈1.65) meets this requirement. Moreover, the aperture below the SIL can further limit the spot size. However, in traditional etching methods to form the aperture, once over-etching occurs, the aperture size becomes larger than the expected. The etching process is hard to be recoverable. Therefore, in 2001, Lane has developed the over-electroplating methods (ISOM, 2001, pp.252-253) to make a tiny aperture in order to improve the disadvantages of the etching methods.
As described above, it is necessary to integrate the SIL with the aperture together to form an excellent optical read/write head so as to achieve a high density optical storage technology. Kate, et al, in 2001, reported a small-sized near-field optical head structure with high throughput. The device combined the SIL and aperture. However, the parts were fabricated separately. After that, the individual part should have to be precisely aligned and bonded. In addition, the planar microlens was far apart from the aperture. The refraction index of air between the microlens and aperture would influence the NA and quality of focused spot.
U.S. Pat. No. 6,335,522B1, entitled xe2x80x9cOptical Probe Having a Refractive Index Micro-Lens and Method of Manufacturing The Samexe2x80x9d, Asimada, et al, published on Jan. 1, 2002 disclosed an optical probe having a movable end arranged on an elastic body and a micro-lens with refractive index adaptive for focussing light in an aperture. The method of which is to fabricate aperture and SIL on two substrates individually, and then combine these two substrate together to accomplish the assembly of the element. The disadvantages include that the alignment exists error and the configuration is hard to be obtained in consecutive steps.
U.S. Pat. No. 6,154,326, entitled xe2x80x9cOptical Head, Disk Apparatus, Method For Manufacturing Optical Head, and Optical Elementxe2x80x9d, Ueyanagi; et al, published on Nov. 11, 2000, and U.S. Pat. No. 6,055,220, entitled xe2x80x9cOptical Disk Data Storage System With Improved Solid Immersion Lensxe2x80x9d, Mamin, et al, published on Nov. 11, 2000, disclosed optical apparatus having aperture. The disclosed methods need to use a high resolution apparatus, such as Electron beam or FIB (Focus Ion Beam), to define the aperture size. Therefore, it needs expensive instrument to accomplish this manufacturing process. In addition, there have no further technology disclosed for the shrinkage of the finished aperture.
As shown in FIG. 2 and FIGS. 3A to 3D which illustrate the conventional process for manufacturing SIL and metallic aperture. In these drawings, FIG. 2 is a schematic drawing showing a combined SIL and aperture which are fabricated separately and then combined together, and FIGS. 3A to 3D are cross section views showing manufacturing process steps of the device of the FIG. 2. As shown in these figures, the reference numeral 17 represents silicon substrate, 18 indicates film such as SiN, 19 is Al layer which is deposited on the film. In these conventional process, a combined SIL and aperture is manufactured by using FIB technique to cut away the material to make a small square shaped aperture, and then attaching a SIL on the rear side of the film. As described above, besides the process utilizes the expensive instrument to define the aperture, it does not provide any technology for the shrinkage of the aperture. Moreover, the SIL and aperture are manufactured separately, and after that, they are combined together. Thus, the process is inconvenient and costly.
Therefore, a manufacturing process is developed here to combine SIL and aperture, which is much simpler than the current process for the fabrication of the aperture without any special instrument, and capable of making a complete element by using current available semiconductor manufacturing process in continuous process steps without assembling.
In view of the above described conventional problems, the object of the invention is to provide an integrated method for manufacturing a combined solid immersion lens (SIL) and submicron aperture, and device thereof, which incorporates photoresist reflow and electroplating to combine a microlens structure with a nanometer order of aperture in order to manufacture an optical read/write apparatus having solid immersion lens and nanometer aperture with high resolution so as to increase optical storage density, and device thereof. The method just uses two photomasks and can be processed in batch, such that the yield and accuracy can be promoted.
To achieve the above object, according to one aspect of the invention, an integrated method for manufacturing a combined solid immersion lens (SIL) and submicron aperture is provided, comprising the following steps: (i) providing a substrate; (ii) depositing a sacrificial layer on the substrate; (iii) coating a first photoresist layer on the sacrificial layer, and using photoxe2x80x94lithography to pattern the first photoresist layer to define an initial aperture; (iv) performing reflow process on the first photoresist layer to make edge of the aperture round and smooth and form a cone-shaped aperture; (v) performing over-etching process to remove the sacrificial layer below the aperture; (vi) depositing a conductive material on the reflowed first photoresist layer as a current conducting layer; (vii) performing electroplating to reduce the aperture size; (viii) coating a second photoresist layer on the electroplating layer, and using photo-lithography to pattern the second photoresist layer to define a cylindrical phtoresist structure, (ix) applying a high temperature thermal reflow to allow the cylindrical photoresist to form a hemi-sphere shaped lens; and (x) removing the substrate.
Further, in accordance with the method of above aspect, the method further comprises steps of using a spin-coating process to coat a third photoresist layer on the substrate after forming the hemi-sphere shaped lens, and using photolithography to make an optical fiber support on the substrate.
Further, in accordance with the method of above aspect, the first photoresist layer and the second photoresist layer may use the same material, and the third photoresist layer should not use the same material as the second photoresist layer.
Furthermore, according to another aspect of the invention, a device for a combined solid immersion lens (SIL) and submicron aperture is provided, which is arranged between an optical read/write head and a recording media, comprising a solid immersion lens (SIL) and a submicron aperture, wherein the aperture is made of a first photoresist layer by using photo-lithography and the first photoresist layer is coated on a sacrificial layer which is deposited on a silicon substrate, and the SIL is made of a second photoresist layer above the aperture by using photolithography.
Further, in accordance with the device of above aspect, the aperture is made by using reflow process on the first photoresist layer to allow edge of the aperture round and smooth and form a cone-shaped aperture so as to increase an amount of light incident into the aperture.
Further, in accordance with the device of above aspect, the SIL is made by using photo-lithography on the second photoresist layer to form a cylindrical shaped photoresist structure and then using high temperature reflow process on the cylindrical shaped photoresist structure to form a hemi-sphere shaped lens.
Further, in accordance with the device of above aspect, the device further comprises an optical fiber support, made by using a spin-coating process to coat a third photoresist layer, and using photo-lithography on the third photoresist layer.
Further, in accordance with the device of above aspect, the first photoresist layer and the second photoresist layer may use the same material, and the third photoresist layer should not use the same material as the second photoresist
As described, according to the invention, it is capable of using a consecutive manufacturing process to achieve a complete structure without any assembling procedure. That is to say, the invention utilizes the steps of using the photo-lithography to define an initial aperture on the photoresist layer, applying the reflow process to allow the edge of the photoresist layer becoming round to increase the light amount incident into the aperture, then using the electroplating to shrink the initial aperture size to a nanometer order on the photoresist layer, and finally performing the photolithography and reflow process to make an excellent curvature of the microlens on the aperture. Among others, the whole manufacturing process can be accomplished without any special instrument and can also be performed in a batch preocess. Therefore, the fabrication of the aperture of the invention is much simpler than that of the conventional aperture without any dedicated and expensive instrument or any complicated process. Also, the manufacturing method according to the invention can be performed in batch process to prevent errors from the assembling procedure, so the yield and the accuracy can be promoted accordingly.